This invention relates in general to light fixtures and more particularly, to an air-cooled light fixture adapted to emit a narrow spectral energy band from a broad spectral energy band high intensity light source.
Light sources such as seal beam lamps and the like include optical devices which direct the light therefrom along a narrow beam path. These lamps get exceptionally hot when confined to a small area. It is important to operate these lamps at or as near as possible to their recommended operating temperatures. Higher than optimum temperature operation reduces their life span and lower temperatures prevents the inert gas contained in many such lamps from returning tungsten from the bulb wall to the filament coils which blackens the lamp walls causing a reduced intensity output.
In the type of light fixture to which this invention is directed the required temperatures within the fixture vary. The filters must be held within a range of ambient temperatures while the lamp must be operated at a normal high temperature of several hundred degrees Fahrenheit.
In many applications of this type of a source of light from a fixture of this type, a requirement exists for the intensity of the light leaving the fixture to be varied according to the distance of the object to be illuminated, the reflectance factor of the illuminated object and the existing ambient light level. There are light sources that can be adjusted as to intensity levels by the viewer at remote locations. None of the prior art teaches automatic light intensity control at the light source which considers the variables above mentioned. It is particularly important for automatic light control when the light is used to illuminate objects picked up by television means when the objects continually vary as to distance from a few feet to several hundred feet.
U.S. Pat. No. 4,321,659 teaches the cooling of the filters by the use of an ambient air stream drawn through the filters. This system is adequate for cooling the filters used with low or medium powered light sources, but does not teach maintaining different temperatures within the housing, prevent moisture from entering the housing, provide safety shut down of the lamp if lamp temperatures fall outside of their operating perimeter.
There is a continuing need for improvements in light fixture of the type defined.